The present disclosure herein relates to an electrical switchgear, and more particularly, to an electrical switchgear using a metal-insulator transition critical temperature switch.
Typically an electrical switchgear for overcurrent protection is configured with a combination of a magnetic contactor (MC) including an electro-magnet and a thermal overload relay as shown in 10a3 of FIG. 1.
An electro-magnet has a very simple structure and an electromagnetic function by the Lenz law like a coil type solenoid provided by winding a conductive wire around a metal. The electro-magnet becomes a magnet when current flows through the coil and loses the magnetic function when the current stops flowing through the coil.
A magnetic contactor 10a1 is switched on or off on the basis of a force generated by the electro-magnet to allow power to be supplied to or cut off about a power equipment.
On the other hand, a thermal overload relay 10a2 has a structure in which a nichrome wire and a bimetal are serially connected to an operation power line 2-1, which extends through the magnetic contactor 10a1 as shown in FIG. 2. In this case, heat of the nichrome wire 20-2 is delivered well to the bimetal 20-3 according to a type in which the nichrome wire 20-2 is wound around the bimetal 203.
When overcurrent flows through the power line, the bimetal may be bent by the heat of the nichrome wire. Due to the bent phenomenon of the bimetal, as shown in FIG. 3, when a mechanical relay contact is taken off, power supplied from the power line 20-1 to a terminal block 20-4 is cut off. However, when the relay contact is taken on or off, a spark flies between relay contacts. When the thermal overload relay is used for a long time, there are several cases where the spark causes a mechanical contact to incorrectly operate to damage a power equipment connected to the power line. In addition, since the bimetal has a wide bent temperature range, it is difficult to rapidly cut off power and a secular change occurs.
When current of 8 to 12 times greater than rated current flows, since a circuit breaker using mechanical contacts cuts off the current, the cut-off operation actually occurs after the power equipment is damaged.
An earth leakage breaker operates like the circuit breaker and also breaks a circuit after the damage. Accordingly, more precise current management and rapid cut-off are necessary. In fact, as an alternative, there is an electronic circuit for protecting a wire using a method for measuring current with a coil (i.e. current transformer) in order to overcome limitations of the mechanical contacts and bimetal. This is a good improvement but the circuit therefor is complex. Accordingly, a more improved electrical switchgear is desired.